Test declarative WebMCP discovery and invocation

[rgarcia]

Summary

• Add a self-contained reservation form using native declarative WebMCP annotations, toolautosubmit, and SubmitEvent.respondWith; no imperative registration or polyfill.
• Reuse TestPlaywrightExecuteAPI's container and warm daemon rather than adding another container startup. Exercise GET /webmcp/tools and POST /webmcp/invoke for both a top-level form and an embedded frame. Assert synthesized schema, field descriptions, required fields, numeric bounds, select enum, autosubmit annotation, and page/frame provenance.
• Read the DOM through /playwright/execute to verify the field values, visible confirmation, agentInvoked, and exactly one submission. Include fixture documentation and local run commands.

Browser results

The locally built headless image runs Chromium 152.0.7977.42 with its default WebMCP flags. Both variants expose reserve_table with string name/date fields, numeric party size, and seating enum ["dining_room", "terrace", "booth"]. Chromium adds format: "date" and a date-format description hint. Top-level provenance has frame: null; embedded provenance identifies the reservation frame and retains the parent page title/URL.

Both invocations return status: "completed" and output:

{"date":"2030-06-15","name":"Test Guest","party_size":"4","seating":"terrace"}

The visible confirmation contains these values and records one native agent submission. Declarative synthesis works, so there is no unsupported-browser skip.

Validation

• Built the headless image using the documented Dockerfile.
• Passed make test-e2e with GOFLAGS='-run=TestPlaywrightExecuteAPI$ -count=3' against that image, including race detection. Used TESTCONTAINERS_HOST_OVERRIDE=127.0.0.1 because local localhost resolution was unavailable.
• Passed make test-runtime (14 tests).
• Passed go test -race ./lib/webmcpclient ./lib/browsersurface ./cmd/api/api ./lib/oapi.
• make test-unit passed vet and all packages except the existing TestUpstreamManagerDetectsChromiumAndRestart: Chromium's temporary profile cleanup fails with directory not empty, including on retry. No unrelated production code changed.
• Did not run the entire e2e suite or build the headful image.

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